As used herein, the term "durable" with reference to surface modification means wicking performance after wet-processing, such as dyeing, or at least ten launderings that is superior to wicking performance without the surface modification.
As used herein, the term "fiber" includes fibers of extreme or indefinite length (filaments) and fibers of short length (staple).
Thermoplastic polymers are widely used as raw materials in making fibers for the textile industry. The preference for a textile material by consumers depends largely upon a perception of comfort in the textile garment. Garments made from natural fibers, like cotton, are generally perceived to be more comfortable than garments made from synthetic fibers, like polyester. The preference for cotton is due, at least in part, to cotton's ability to wick perspiration away from the human body. Synthetic fibers, in contrast, tend to be hydrophobic and resist water absorption and transport, but are quick drying.
Several processes have been employed to overcome the moisture transport deficiencies of synthetic fibers. U.S. Pat. No. 4,954,398 to Bagrodia et al. describes treating grooved polyester fibers to the extent necessary to provide a specified roughness at the bottom of the groove which is a specified amount higher than the roughness outside the groove. According to the patent, the treatment provides fibers with wetting characteristics.
Japanese Kokai Patent Application No. 56-112535 describes the preparation of a water-absorbing fabric made from grooved fibers. The fibers are each made from two or more types of thermoplastic polymers having different solubilities so that one of the polymers is dissolved to leave the remaining thermoplastic polymer with grooves. Each fiber has at least six grooves which are virtually continuous in the fiber and have a specified width, depth and proportion of the fiber's cross-sectional area. The Kokai alludes to hydrophilic properties used in combination with absorbent capacity but does not explain how the combination is achieved or how the wetting capacity increases in the combination. The Kokai notes that the grooves are formed on the surface of the fibers to take advantage of the capillary effect of the grooves, and concludes that the effect of grooves is favorable to the effect of adding a moisture absorbing additive to the fibers.
Groove-containing fibers are also generally known. For example, U.S. Pat. No. 4,639,397 to Sato et al. discloses a thermoplastic polymer fiber intended to mimic silk. The fiber has at least two axially continuous grooves of specified width and depth along its periphery.
U.S. Pat. No. 5,057,368 to Largman et al. discloses a fiber having three or four t-shaped lobes where the legs intersect at a stated angle. The fiber is said to be useful for diverse applications such as filtering, wicking, insulating, etc.
Fibers advertised as moisture wicking are presently available from E. I. DuPont de Nemours & Company as Coolmax.TM. or Thermax.TM., Allied Chemical Company as Hydrofil.TM., and Patagonia as Capilene.TM.. None of those fibers has the novel structure of the present invention.